In 2004, a Patent to Borchert et al. U.S. Pat. No. 6,822,457 described that a common occurrence in the power distribution industry is an arcing or electrical discharge in the transmission and distribution grid system. Such faults commonly are caused by such as insulation breakdown, physical damage to the transmission line, moisture ingress etc., or a combination thereof, and it is noted, characteristics of an arcing or discharge fault vary widely. For instance, a fault may manifest as a relatively high impedance transient event which lasts for only microseconds, or as a low impedance sustained fault that eventually leads to rupture of network protection devices, (eg. a fuse or circuit breaker or the operation of a circuit breaking relay).
It is to be understood that even minor occurrences of transient discharge in cables can eventually lead to more catastrophic problems because successive discharge events degrade the quality of the cable. Early detection and location of transient fault events, leading to their correction, can therefore result in economic benefits such as increased overall network quality and customer satisfaction because of reduced outages.
Important to the Borchert et al 457 patent is that a consistent characteristic of an arcing or discharge fault event is, at the time of discharge, the generation of a burst of electrical energy or noise which comprises high frequency components. And, it is also important to understand that voltage and/or current waveforms generated by the arcing or discharge fault event travel away from the fault site in both directions in the transmission system. This phenomenon has been disclosed in a number of patents. For instance Biskeborn, U.S. Pat. No. 2,493,800, 1950, Weintraub, U.S. Pat. No. 2,717,992, 1955, Biskip, U.S. Pat. No. 3,462,681, 1969, disclose fault location systems that:                Detect the electrical wave associated with a discharge, partial discharge, arcing fault or lightning strike that travels to each end of the cable or transmission system from the fault point.        Collect time data associated with the traveling wave caused by the fault or event passing a sensor or coupling point at each end of the transmission system.        Calculate distance to fault by centrally processing the time delay data via an RF communications link, or some other data transmission link.Said Patents describe systems for application to high voltage overhead transmission lines, and assume a velocity of propagation of the traveling wave.        
The Biskeborn 800 patent describes an application to shorter cable lengths, but requires access to each end of the cable at a common point.
The Pardis, U.S. Pat. No. 3,609,533, 1971, describes a fault location system which utilizes a high energy pulse transmitted on the network under test to provide a reference for time and/or delay measurements to determine distance to fault, (rather than use of an RF link or other transmission media). The 533 patent generally:                Is applied to high voltage overhead transmission lines;        Is designed for massive insulation breakdown or lightning strike, and provides 500 to 1,000 feet of accuracy; and        Assumes velocity of propagation of the traveling wave.        
A Patent to Maureira, U.S. Pat. No. 5,416,418, 1995, describes application in lower voltage, (ie. 6 kV to 33 kV), distribution cables, and focuses on partial discharge events using a pulse transmission technique as a reference/timing signal. The general characteristics of the Maureira invention are:                It is designed for application on shorter power distribution networks than is the Pardis 533 patent system;        It detects much smaller partial discharge or corona discharge faults, (partial discharge faults are periodic, non-catastrophic corona discharge events), that don't necessarily trip circuit breakers or destroy the cable, but do degrade the cable over time;        It requires the cable to be isolated from the distribution network;        It requires a high voltage source to stress the cable into partial discharge activity; and        It assumes velocity of propagation or uses a VOP established during test setup.        
Considering previous disclosures and the economic benefit associated with locating faults in a proactive manner, it is apparent that clear commercial advantage can result from application of new technology which provides low cost, accurate fault location methods and apparatus, thereby providing improvement over previously disclosed systems. Characteristics of such a method and apparatus as disclosed in the Borchert et al. 457 patent include:                It monitors and stores the established phenomenon of a traveling wave emanating from an arcing or discharge fault in the time domain,        It co-ordinates the monitoring invention(s) in a manner that allows ratio-metric time to distance calculations versus a known distance between the monitoring systems based on traveling wave time delay measurements and initiating signals,        It improves upon Biskeborn, Weintraub, Biskip, and Pardis, by providing more accurate, higher resolution timing measurements, which, in turn, increase the accuracy of distance to fault calculations,        It improves upon Maureira by allowing the transmission system to remain in service for fault locating,        Unlike the Maureira 418 patent system, there is no requirement that an external, (other than that intrinsic to the distribution system), high voltage be applied to sufficiently stress the transmission system to cause discharge.        
A Patent to Bjorklund, U.S. Pat. No. 5,903,155 describes the same fundamental process that Biskeborn, Weintraub, Biskip, Pardis and Maureira use, namely:                Detecting the traveling wave produced by a fault by at least two receivers on each end of the transmission system;        Synchronize the timing of the traveling wave reception via some method so distance to fault calculations can be made.The specific claims of the Bjorklund patent are:        It specifies High Voltage DC transmission system in the claims;        It uses synchronous clocks at each receiver; and        It detects current associated with the traveling wave using a DC transformer and a Rogowski (AC) coil. Previous patents also detect the current.        
A Patent to Wright et al U.S. Pat. No. 4,499,417 describes a single ended system that uses the disturbance created by the fault and subsequent reflections. In summary;                It detects the first instance of a disturbance created by a fault in either voltage or current;        It identifies and labels that particular event using either voltage or current characteristics;        It continues to analyze the transmission line comparing subsequent events to the first using the characteristics as above or predicted characteristics based on knowledge of the transmission line;        It measures time taken for the disturbance to travel from initial characterization, travel to the fault and back as a reflection;        It determines distance to the fault based on time measurement data; and        Distance to Fault calculations are based on a signal propagation velocity constant determined by the type of transmission line.        
A Patent to Bunch U.S. Pat. No. 4,570,231 describes the same fundamental process that Biskeborn, Weintraub, Biskip, Pardis and Maureira uses, namely:                It detects the traveling wave produced by a fault by at least two receivers on each end of the transmission system;        It synchronizes the timing of the traveling wave reception via some method so distance to fault calculations can be made;The specific claims of the Bunch patent are:        It comprises a fault finder for locating fault on a high voltage transmission line;        It provides improved filtering to reject background noise to allow easier identification of a fault;        It synchronizes time delay measurements using a conventional modem communication link between the two receiving stations.        
A Patent to Burnett U.S. Pat. No. 5,243,294 discloses a complex system for determining the likelihood of a physical anomaly in an elongate, electrically conductive member, such as an oil or gas pipeline. The technique is based on sending two pulses from either end of the physical body to be evaluated. Further,                It synchronizes the two pulse generators at either end of the physical body so that the collision point of the two pulses traveling from each end can be predicted;        It scans the collision point of the pulses along the physical body; and        It evaluates the characteristics of the collision of the waves to determine the probability of a physical anomaly.        
A Patent to Bellis et al U.S. Pat. No. 4,491,782 describes improvement to Time Domain Reflectometry, also known as Pulse Echo. This patent is targeted to unstable, transitory faults, as well as stable faults in energized power cable. It discloses:
Continuing, a TDR technique for power transmission lines is characterized by;                It uses current or voltage sensors to determine if a fault is occurring;        It stores a series of before fault and after fault TDR waveforms; and        It compares the healthy TDR waveforms to the faulty TDR waveforms to aid in discerning the fault location.        
A Patent to Walsh U.S. Pat. No. 5,382,910 describes improvement to Time Domain Reflectometry by canceling out the blind spot or dead zone inherent in any TDR system during the transmission of the test pulse.
A Patent to Oberg et al. U.S. Pat. No. 5,751,149 describes improvement to Time Domain Reflectometry by implementing a very high and adjustable frequency transmit pulse to allow frequency sensitive faults to be more visible to the TDR.
A Patent to Westwood U.S. Pat. No. 5,514,965 describes improvement to Time Domain Reflectometry by using new technology, a digital, programmable delay generator device as a TDR timebase to improve resolution of fault reflections.
Continuing, in some cases, such as where a low voltage power is distributed to residences and industry, it can be hazardous to public safety to apply any form of high voltage. Further it is desirable to allow customers to continue to be served with power while a system is being tested. In that light it is noted that the presently disclosed invention uses the AC signal being distributed as the source of its signal, (emphasis added). This improves upon the Maureira 418 patent approach, (which may actually create a fault at a previous non-faulted site), by not further damaging the transmission system with a high voltage source. The presently disclosed invention also determines a velocity of propagation, which is used for distance calculations, at an instant just before a fault occurs, which improves accuracy because velocity of propagation can change with cable type, age, time, power loading and ambient temperature. The presently disclosed invention further initiates invention system data storage before a fault, rather than after a fault. This is beneficial because where a fault is catastrophic enough to create a complete open or short circuit, an initiating signal path does not exist.
At this point it is disclosed that the Borchert et al 457 Patent invention improved upon all the cited prior art by providing initiation of invention system operation before a fault, rather than after a fault. This is important as velocity of propagation can be affected by AC power current loading over time and fault current. Further, the Borchert et al 457 patent disclosed invention provides an initiating signal in the form of a coherent spectrum that can be filtered and amplified to increase resolution and/or noise immunity.
Even in view of the known prior art, there remains need for a system and method and system for identifying magnitude vs. time matrix of data relating to waves launched onto an electric signal transmission medium, to provide insight into the nature of the signature of the said electric signal transmission medium.